OS105 HZR runs super rich (problem solved)

[rebeltrousers]

Question: Should I compensate on my mid-needle as well, or just the high when the HZ stem arrives?

[CyprusFlyer]

Mid needle should respond as normal, once you have the high tuned then the correct amount of fuel should be available for the mid needle tuning. Just follow Tim Jones's videos and all should be good. The mid should be in the recommended ballpark though.

[rebeltrousers]

Great, thanks heaps!

[duckmansweb]

righto ive got my new 105HZ-R today , i think its an old version , has threaded muffler holes and marks on the carb for Low-Mid-Full , my needle holder measures 1.7mm , aparantly the older version dont have an issue with the needle holder, i have a needle holder from a 91HZ , its alot smaller the hole would be 1.3mm, bit confused if ive got a good one or a bad one

[Glenn Goodlett]

I think they all have threaded muffler holes. I could be wrong though.

[rebeltrousers]

Will post back after I fly tomorrow!

[duckmansweb]

i just ordered one of them also from tower

[rebeltrousers]

Well.....
It allowed me to lean the motor, managed to get to a temperature where the backplate was uncomfortable to touch for more than a couple of seconds. No really noticeable increase in power (or more stable rpm) for the trade-off in heat so I went back to the standard setup and will continue to run at around 3/4 of a turn out on both needles.
I think realistically I'm asking quite a lot of the 105HZR with 813 blades!

[duckmansweb]

so you have gone back to the 29088940 needle holder ?

[rebeltrousers]

Yeah just the normal one that comes with the motor. Probably a bit different with me running 800-size I reckon.....

[marc8090]

From what I've seen, you will have all sorts of tuning issues trying to swing such long blades at "normal" headspeeds with "normal" amounts of pitch. You're simply placing to much of a load on the engine.

[rebeltrousers]

Yes that's correct. I think if I just scale everything back a little I'll be ok!

[duckmansweb]

not sure about this rich issue you guys are saying , i flew a few break in tanks yesterday at 2 turns on main and 1 on the high with 15% and the stock 0.20mm shim , Ive got the main at 2 clicks less than 1.5 turns out and the mid at .75, its just starting to come on song, but not so rich its hopeless , the thing is an animal, will keep it there for a few more tanks yet , ive also got the 1.7mm larger needle holder and im at sea level

[Rodney Kirstine]

Being at sea level is what's really helping you out. I'm at about 2700 ft above sea level and flying my 105 is a sputtering bog-fest. The only time that it's run really clean and strong was when the temperature was below freezing.

[Stevin]

Ordered the part number listed above and installed it. The motor would not even run. After calling os, a rep said the part is for the non regulated version. I told him about this whole thread and he said that he knows nothing of a new needle seat.

[rebeltrousers]

It's not really good enough is it....

[Sirolf]

What about the main needle assembly of the 91SZ pumped engine?
This one also doesn't close fully and the hole measures 1.3mm.

HZ-R is on the left, SZ on the right. It looks like one is longer than the other but their the same.
I test fitted it and fits nicely, just don't have the time yet to try it.

[duckmansweb]

After much testing I have found what this motor likes , the needle holder must be the one from the 91PS 21981941 , the 91hz one is too small and does not allow the Neg pressure to allow the regulator to operate properly , and the HZ-R one is too big 1.7mm , what works for me is the os91 PS needle valve holder 21981941 and the needle from the 105hzr , fuel I found best is 21% c.p l.v , 18% nitro , 0.20 head shim , I can pull 14deg pitch , at sea level , 2 turns out on the main and 1.5 on the mid , the mid needle responds normally now and FYI the hole in the 21981941 holder is 1.6mm

[Rob43]

This whole thread has soured me on the $530 it takes to buy in. Has this only affected a few engines, or is it widespread? I've not been thrilled with O.S. response. I know they make superb engines, but not sure what to make of this.

[Rodney Kirstine]

There is still no official word on a change being made. All of the 105hz-r's have shipped with the 1.7mm dia needle seat, from what they told me. I don't fly mine hardly at all, I fly the 91srx mostly.